This invention generally relates to oil and gas well logging and, more particularly, to an apparatus and method for deploying fiber optic cabling and profiling the temperature of the well using the fiber optic cable.
Oil and gas exploration is a risky, complex task that involves sophisticated equipment and substantial financial resources. Whether on land or at sea, a search for oil and gas commences with the drilling of a well. A well may reach a depth of over a mile, or, in the case of ultraheavy rigs, may reach more than six miles in depth.
Once a well is drilled, a technique known as well logging (or wireline logging) provides valuable information about the well, specifically about the likely presence of hydrocarbons nearby. Traditionally, wireline logging was performed by lowering a measuring device known as a sonde down the well. A sonde is a metal container, usually a cylinder, which contains various instrumentation used to gather data.
The wireline sonde is lowered to the bottom of the well, at the well bore. Measurements are taken by the sonde as it is being lifted back to the surface of the well. The types of measurements taken may vary widely. Examples of measurements that may be performed include natural radiation emission, reaction to gamma ray or neutron bombardment, sonic, electrical, electromagnetic induction, resistivity, and so on.
With multiple instruments contained within, the sonde is typically heavy enough to be dropped down the well on a cable or wire. The sonde may be pulled back to the surface using a wench or a pulley.
Recently, fiber optic cable has been used as an alternative for obtaining valuable well data. Fiber optic cable may be advantageous because data can be transmitted at a high speed over long distances. Fiber optic cable is non-conductive and thus may be preferable to use in the well over electrical or electromechanical instruments because of the presence of explosive hydrocarbons.
Better yet, the measurements obtained using the fiber optic cable may be immediately transmitted up the well to a receiving system, such as a portable computer. Using techniques such as optical time domain reflectometry (OTDR), fiber optic cables have, in many cases, supplanted traditional mechanisms for obtaining data within the well bore. Transmitting fiber optic cable down a well under pressure, however, may be problematic.
Thus, there is a need for a method of delivering fiber optic cable down a well under pressure.
In accordance with the embodiments described herein, a wellhead spool is disclosed comprising a connection to a well head, a sealed spool for storing fiber optic cable to be disposed down a well bore, and an anchor coupled to the fiber optic cable, wherein the anchor is placed in an opening of the well head and the fiber optic cable is released from the spool. In one embodiment, the wellhead spool comprises a motor, preferably hydraulic, coupled to the spool to both release the fiber optic cable from and to return the fiber optic cable to the spool. In a second embodiment, the wellhead spool comprises a solvent dispersal tube to clean the fiber optic cable upon return to the spool. In a third embodiment, the wellhead spool comprises a safety valve for equalizing the pressure between the wellhead spool and the well bore.
In another aspect of the invention, a method is disclosed comprising mounting a wellhead spool providing a fiber optic cable in a sealable housing, coupling the fiber optic cable to an anchor, engaging the sealable housing to a well head, opening a valve to the well bore, deploying the anchor and fiber optic cable into the well bore, and coupling the fiber optic cable to a measuring instrument. The method further discloses dispersing a solvent upon the fiber optic cable and engaging the anchor to a wall of the well bore.
Furthermore, in another aspect of the invention, a method and apparatus to profile the temperature of a wellbore using a fiber optic cable and an anchor is disclosed. Particularly, the apparatus and method include mounting an anchor to a fiber optic cable and deploying the combination downhole to anchor and take measurements at desired depths of investigation. More specifically, a method for measuring the temperature of a wellbore at multiple depths of investigation using a fiber optic cable and an anchor is disclosed.